1. Field of the Invention
The present invention relates to a stabilizer for chlorine-containing resins which is non-toxic, which serves to prevent secondary aggregation of the resins while they are being shipped, and particularly which improves the workability of the resins, and further to a process for producing such stabilizers.
2. Description of the Prior Art
Examples of chlorine-containing resins used in this invention include, for example, polyvinyl chloride, most commonly commercially available with a chlorine content of around 56.6 wt%; polyvinylidene chloride, most commonly commercially available with a chlorine content of around 73.2 wt%; a' vinyl chloride-vinylidene chloride copolymer; a vinyl chloride-vinyl acetate copolymer, most generally commercially available with a vinyl acetate content of 0.4 to 40 wt%, more often 0.5 to 20 wt%; a vinyl chloride-ethylene copolymer, most generally commercially available with an ethylene content of 1 to 15 mole % and a mean molecular weight of 700 to 1500; chlorinated vinyl chloride, most generally commercially available with a chlorine content of 60 to 70 wt%, more often 63 to 68 wt%; and chlorinated polyethylene, most generally commercially available with a chlorine content of 25 to 45 wt%. These materials undergo thermal decomposition during molding, and require a stabilizer to prevent such thermal decomposition. As later will be explained in detail, the present invention provides such a stabilizer.
Heretofore, inorganic acid salts, organic acid metal salts, and organic tin compounds have generally been used as such stabilizers.
Many of these stabilizers are toxic, e.g., those which contain lead, and accordingly their use is limited. Recently, non-toxic calcium hydroxide which has thermal stability and is very inexpensive has come into popular use.
However, particulate calcium hydroxide does not have a smooth surface, so that when the particulate calcium hydroxide or a chlorine-containing resin powder containing such particulate calcium hydroxide is shipped, or particularly when it is automatically fed, the calcium hydroxide aggregates (this phenomenon will hereafter be referred to as secondary aggregation). This phenomenon eventually degrades the dispersibility of the calcium hydroxide in the chlorine-containing resin powder, or degrades the quality of molded products made of such a mixture of a higher proportion of the products must be rejected as unacceptable, because the calcium hydroxide migrates to the surface of the molded products or adheres to metal molds.